The long-term objective is to investigate to what extent "special" versus "general" processing mechanisms contribute to human speech perception. The specific aims are to study the perception of trading relations in English phonology by humans and monkeys. A trading relation is one in which multiple, and seemingly unrelated, acoustic cues contribute to the same phonetic percept. Trading relations are studied by synthesizing both normal and altered speech sound continua in which the value of one acoustic cue is reduced. Listeners perceive a shift in the identified phoneme boundary to compensate for the reduced cue. Both general mammalian auditory and human-specific, articulation-mediated processes have been proposed to account for trading relations. The comparative approach is a powerful tool to help distinguish between these two alternatives. We propose to train two different monkey species to identify speech sounds using both go/no-go and go-left/go-right procedures in order to test their sensitivity to trading relations. Monkeys will be trained with operant conditioning techniques and positive (food) reinforcement. Two human subject populations consisting of both native American and non-native (Hispanic) speakers of English will be tested with the same basic procedures. Comparisons between these subject groups will help to clarify if trading relations are native- language-specific, human-specific, or reflect general processing strategies of the primate auditory system. Results will be related to a theoretical framework put forth by developmental psycho-linguists that distinguishes between "maintenance", "facilitation" and "induction" as different processes by which linguistic experience affects speech perception.